A software RAID controller is a system that manages multiple hard drives to improve performance and data redundancy without the need for dedicated hardware. It uses the computer's operating system to combine several drives into a single logical unit, allowing for various configurations like RAID 0, RAID 1, or RAID 5. This approach is often more cost-effective than hardware RAID solutions. Unlike hardware RAID controllers, which have their own processors, software RAID relies on the main CPU to handle data management tasks. This can lead to slightly reduced performance under heavy loads, but it offers flexibility and easier configuration through the operating system, making it suitable for many users and applications.